Sheet metal pipe geometry for minimum pressure drop in a heat exchanger

ABSTRACT

A heat exchanger joint between a pipe and a header wall defines an endless transition for conveying the heat exchange medium closely over a control surface of a radius or a chamfer between the interior surface and the pipe to reduce turbulence and pressure loss. The radiused or chamfered flow control surface expands radially as it opens axially into the interior surface of the header wall.

FIELD OF THE INVENTION

This invention relates to automotive heat exchangers in general, andspecifically to a liquid flow heat exchanger, such as a radiator, with anovel in tank structure for reducing the pressure drop caused by flowturning losses.

BACKGROUND OF THE INVENTION

Automotive heat exchangers that use a pumped, liquid heat exchangemedium, as opposed to a compressed gaseous/liquid heat exchange medium,include radiators and heaters. Typically, these include two elongatedmanifolds or header tanks, one on each side of the heat exchanger, witha central core consisting of a plurality of evenly spaced, flattenedflow tubes and interleaved corrugated air fins running between the twotanks. Each tank is generally box shaped, with parallel side walls, aback wall joining the side walls, two axially opposed ends, and an openarea opposite the back wall, which is eventually closed off when it isfixed leak tight to one side of the core. Each header tank distributespumped liquid to or from the flow tubes in the core, and is in turnfilled or drained by an inlet or outlet pipe opening into the headertank at a discrete location. In typical radiators, the inlet or outletpipe to the header tank is oriented both transversely to the length ofthe tank and to the flow tubes. Coolant flow entering the inlet pipemust, therefore, turn through a substantial angle toward the two ends ofthe tank before as well as turning substantially again to flow out ofthe tank interior and into the flow tubes. The converse is true forcoolant exiting the return tank through the outlet pipe. An example of arecent radiator with molded plastic, box shaped header tanks may be seenin U.S. Pat. No. 5,762,130, which is fairly typical in its basic flowconfiguration, apart from being a U flow design, with the inlet andoutlet pipe located on one tank. The orientation of the pipes relativeto the tank walls and flow tubes is as described above, however. A metaldesign is shown in U.S. Pat. No. 6,283,200 wherein the end of the inletpipe is flared outwardly to reduce the pressure loss.

The design of a radiator or any cross flow heat exchanger with a liquidmedium flowing in one direction through flow tubes, and with air blownperpendicularly across the flow tubes, is a compromise between heatexchange efficiency between the two flowing media, and the pressure orpumping losses of the two media. For example, it is well known thatdecreasing the flow passage cross sectional area will present relativelymore surface area of the fluid medium within the flow passage to the airblowing over the flow tube, increasing the heat transfer efficiency fromfluid to air. A tube that is smaller on the inside is also thinner onthe outside, and so presents less obstruction the air blown over theoutside of it, decreasing the air side pressure loss through the core.However, a thinner flow tube creates more fluid pressure loss throughthe tube, end to end. Some compromise can generally be found betweenairside pressure drop, tube thickness, and liquid (coolant) pressuredrop. However, the ability to reduce total coolant pressure loss(pumping loss) elsewhere in the heat exchanger would allow the use ofthinner tubes in general, which would be very positive, considering thatthinner tubes also decrease air side pressure loss.

One source of coolant pressure drop through the heat exchanger that hasnot received a great deal of attention in the prior art is turbulence or“turning” losses that occur at the transition between the pipe openingand the enclosed interior of the header tank. That is, since the inletpipe typically enters through a tank side wall, and not the tank backwall, it is oriented transversely to the flow tubes, as well, and mustchange direction both to reach the opposite ends of the tank and inorder to flow into the tubes. The turning transition is not a greatsource of pressure loss when the interior volume of the tanks is large,since a large interior volume can act as a large pressure reservoir to“absorb” and distribute coolant to the flow tubes. As availableunderhood space shrinks, however, radiator header tanks become smaller,and the parallel sidewalls become closer. Flow exiting the opening ofthe inlet pipe (through the first side wall) impinges on the proximate,opposed second side wall, creating turbulence and pressure loss beforeit can be distributed toward the opposite ends of the tank and into theflow tubes.

The other liquid medium heat exchanger typically found in an automobile,the heater core, has a similar cross flow configuration, but faces adifferent problem. There, the inlet pipe generally opens through theback wall of the header tank, in line with, rather than perpendicularto, the flow tubes. The flow thus impinges directly onto the ends of thenearest aligned flow tubes, rather than against a sidewall of the tank,which would theoretically be positive, in terms of direct flow into thetubes with minimal pressure loss. However, the fact that the ends of thenearest tubes are in line with the inlet pipe is a detriment, becausethe force of the impinging flow against the near tube ends causeserosion and damage. Therefore, it has been proposed in several heatercore designs to place a protective tent or baffle like structure betweenthe inlet pipe opening and the ends of the nearest aligned flow tubes.These act as a road block, in effect, interrupting the flow at thatpoint, rather than smoothing it out, and would actually increase totalcoolant pressure drop across the core. This is an acceptable price inthat context, however, since it is considered necessary to protect theotherwise eroded tubes. Another solution is shown in U.S. Pat. No.6,116,335 to Beamer et al wherein a flow turning structure is moldedinto the inlet header tank opposite to the inlet pipe.

Design of tanks and manifolds in automotive heat exchangers such asradiators involves tradeoffs between the conflicting requirements ofminimizing coolant pressure drop and packaging space. Market trends aresimultaneously driving down the allowable tank size and pressure drop.This problem is further compounded when internal oil coolers or bafflesare required that partially block the inlet/outlet pipes.

Plate type oil coolers are frequently incorporated in radiator tanks toprovide engine and transmission oil cooling. Due to packagingconstraints, it is common for oil coolers to straddle the coolantinlet/outlet pipes. This flow blockage increases coolant pressure dropand creates local regions of high coolant velocity that can causeerosion corrosion of the oil cooler. In a typical cross flow radiator,the tanks and oil cooler represent 50% of the total coolant pressuredrop. The penalty due to the oil cooler blockage is 35-40% of the tankpressure drop (˜20% of total pressure drop).

Since the pipe diameters are specified by the vehicle manufacture, themost common method used to limit the oil cooler coolant pressure droppenalty is the spacing (stand off height) of the oil cooler from theinside tank wall. Typically it is not practical to reduce the pressuredrop penalty below the levels described above because the increasedstand off height required will reduce the size of oil cooler that can beinstalled in the tank, or a larger tank must be used with increasedpackaging space, mass, and cost penalties.

For sheet metal tanks and pipes, the internal juncture between the pipeand tank is typically sharp edged. Due to the joint design, the pipe isfrequently extended into the tank to allow secure clinching of the pipeto the tank. Both the sharp edge and pipe extension act to increasecoolant pressure drop.

SUMMARY OF THE INVENTION AND ADVANTAGES

The subject invention provides a radiator header tank to pipe joint thatreduces coolant pressure drop by reducing turning losses at thetransition between the pipe and the header tank wall.

The heat exchanger assembly of the subject invention is distinguished bya transition between the header wall and the pipe extending transitioncompletely around the opening to present an expanding flow controlsurface between from the header wall to the pipe for conveying the heatexchange medium closely over the control surface between the tankinterior and the pipe to reduce turbulence and pressure loss at thetransition between the tank interior the said pipe.

This invention provides a transition to significantly reduce the oilcooler pressure drop penalty and/or reduce the size of the tank. Amethod of determining the required feature size and practical designsare provided for integrally molded or fabricated sheet metal tanks.Several configurations are shown that incorporate an internal radius orchamfer to eliminate the pipe extension inside the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a fragmentary view of a heat exchanger showing a header tankand heat exchanger core;

FIG. 2 is an interior perspective view of the heat exchanger header tankof FIG. 1;

FIG. 3 is schematic showing the flow pattern for a sharp edged pipe toheader joint of the prior art;

FIG. 4 is schematic showing the flow pattern for a chamfered header topipe transition of the subject invention;

FIG. 5 is a schematic view comparing the radius and chamfered joints ofthe subject invention; and

FIG. 6 is a perspective view of a header tank incorporating an oilcooler facing an inlet configured in accordance with FIG. 4;

FIG. 7 is a plot of the chamfer/radius size versus the pressure drop fora given inlet diameter;

FIG. 8 is a plot of the taper angle versus pressure drop with a givenchamber angle and pipe size;

FIG. 9 is a plot of chamfer versus pressure drop for various pipediameters and stand off heights;

FIG. 10 is a plot of radius versus pressure drop for a given pipe sizeand various stand-off heights;

FIGS. 11 through 16 show various pipe to header joints constructed inaccordance with the subject invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A heat exchanger assembly constructed in accordance with the subjectinvention is generally shown at 20 in FIGS. 1 and 2. The assembly 20includes a core comprising a plurality of flow tubes 22 having heatexchange fins 24 extending therebetween. A header tank 26 distributes aflowing liquid heat exchange medium to and from the flow tubes 22 andpresents a header wall 28 with an interior surface. A pipe 30 isdisposed in an opening through the header wall 28.

A joint extends between the pipe 30 and the header wall 28 to define anendless transition completely around the opening to present an expandingflow control surface between the pipe 30 and the interior surface 32 ofthe header wall 28 for conveying the heat exchange medium closely overthe control surface between the interior surface and the pipe 30 toreduce turbulence and pressure loss at the transition between theinterior surface and the pipe 30.

A typical pipe to header wall joint is shown in FIG. 3 wherein a sharpedged corner is presented annularly about the opening into the headerwall 28. The pipe is formed in a cylindrical shape to define entry flowinto the header as cylindrical. However, it is to be understood that thecylindrical pipe could be flattened into an oval, elliptical, or othershape at the joint. The joint of the subject invention presents anexpanding flow control surface with a rounded radius 32 or a straight orconical shaped chamfer 34 as illustrated in FIG. 4. The use of a chamfer34 is slightly more effective than the radius 32 due to increasedentrance flow area for the same size pipe flow area as shown in FIG. 5.

The typical pipe/tank juncture is a sharp edged corner as illustrated inFIG. 3. The limiting entrance flow area into the pipe is a cylinder.This invention replaces the sharp corner with a radius or chamfer toincrease entrance flow area and facilitate turning of the flow into thepipe. Flow streamlines for both sharp and chamfered geometry's are shownin FIGS. 3 and 4. Use of a chamfer is slightly more effective than aradius due to increased entrance flow area for the same size feature asshown in FIGS. 5 and 7. The optimum chamfer angle was found to be 45° asshown in FIG. 8.

Based on CFD simulation and prototype testing it was found that theeffect of radius/chamfer size is similar through out the practical rangeof pipe and standoff sizes. A radius/chamfer of 2.0 mm yieldsapproximately 50% of the total savings possible as shown in FIGS. 9 and10. Therefore this invention claims the use of a radius or 30/60°chamfer equal to or greater than 2.0 mm.

Accordingly, the pipe 30 is cylindrical about an axis and the flowcontrol surface expands radially as it opens axially into the interiorsurface 32 of the header wall 28, it expanding through a radius orthrough a cone shaped chamfer. The header wall 28 presents a planardisk-like portion immediately adjacent to and extending radially fromthe opening in the header wall 28 to define the interior surface 32 in aradial plane. In all cases, the control surface blends into the planardisk-like portion to present a smooth transition of the control surfacefrom the pipe 30 into the interior surface 32 of the header wall 28. Itis important that the control surface blend into the planar interiorsurface 32 to present a smooth transition of the control surface fromthe pipe 30 into the interior surface 32 of the header wall 28. Asalluded to above, the control surface may extend through a radius 32 orthrough a cone to define a chamfer 34.

Referring to FIG. 6, the pipe 30 is integrally formed of plasticmaterial with the header wall 28 define the chamfered control surface 34that expands to the radial plane of the interior surface 32 of theheader wall 28. An oil cooler 36 is disposed opposite to the pipe 30.The chamfer 34 significantly reduces the pressure drop caused by theimposition of the oil cooler 36.

Referring to FIGS. 11-16, the header wall 28 defines the control surfaceand the control surface expands from a cylindrical collar 40 to theradial plane of the interior surface 32. Said another way, the headerwall 28 extends through a transition control surface into a cylindricalcollar 40, which receives the pipe 30.

In the FIGS. 11 and 12, the pipe 30 extends within the opening of thecollar 40 and terminates in an annular edge 38. The header wall 28extends into the axially extending collar 40 to surround and engage thepipe 30. The pipe 30 includes a bead 42 abutting the open end of thecollar 40.

Accordance with the invention, the pipe 30 has an end which terminatesin spaced relationship to the radial plane in the header wall 28.

In FIGS. 13-16, the pipe 30 is disposed about the exterior of the collar40.

In FIG. 13, the pipe 30 is flared 48 outwardly into a flare to engagethe exterior of the collar 40 defining the control surface.

In FIGS. 14 and 15, the pipe 30 includes an enlarged end 50 defining ashoulder 52 for surrounding and engaging the exterior of the collar 40with the shoulder 52 abutting the collar 40. The only difference in FIG.15 is that the pipe 30 and the collar 40 are forced radially into oneanother to create a mechanically overlapping connection in the axialdirection.

In FIG. 16, the pipe 30 and the collar 40 include mating undulations 54extending annularly thereabout for locking the pipe 30 to the collar 40to create a mechanically overlapping connection in the axial direction.

It is to be understood that the various embodiments may employ theradius 32 shown in FIGS. 12-14 and 16 or the chamfer 34 shown in FIGS.11 and 15 and that either may be used with the various species of FIGS.11-16. The joint may be formed with a radiused or chamfered flange andmay be secured by fixturing, staking, tack weld, or spin welding, priorto final bonding. The pipe 30 end may be expanded to engage the outsidesurface of the collar or flange 40 as illustrated in FIGS. 11-12. Afeature can be added to the end of the pipe 30 to provide lead in.

The pipe 30 and the header wall 28 may be molded of an organic polymericmaterial (plastic) or formed of sheet metal, when of metal, the pipe 30may be secured to the tank 26 prior to brazing by expanding the collar40 into the pipe 30. Alternately, as illustrated in FIGS. 13-16, thepipe 30 can be a press fit on to the collar 40, or can be shrunk ontothe collar 40. Either the collar 40 or the pipe 30 can be tapered tocontrol the press fit characteristics. The collar 40 can be expandedinto the pipe 30 or the pipe 30 shrunk on to the collar 40. The bead 42may be formed into the pipe 30 and the collar expanded into the bead 42.All configurations allow the use of an unclad pipe 30 and externallyclad tank 26. All configurations are designed to allow brazing of thepipe 30 and collar. Typically clad material is used for the tank 26 bodyand bare material for the pipe 30, but either or both parts can be clad.Alternately, a separate source of braze material can be used such as abraze ring or braze paste. Some of the configurations could also be spinwelded. In the case of plastics, the pipe 30 may be mechanicallyattached or bonded to the collar 40, as by an adhesive, fusion or spinwelding or integrally molded.

The collar 40 and the pipe 30 may be bonded together by brazing,soldering, welding or an adhesive, depending upon the composition of thecomponents. In addition, the pipe 30 may be secured prior to bonding tothe collar 40 by fixturing, a press fit, e.g., expanding or shrinking,staking, forming undulations, etc. In order to facilitate assembly, thepipe 30 and/or collar 40 may include a lead-in such as a taper, or thelocating bead 42 or shoulder 52.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. The invention may bepracticed otherwise than as specifically described within the scope ofthe appended claims.

1. A heat exchanger assembly comprising; a plurality of flow tubes, aheader tank for distributing a flowing liquid heat exchange medium toand from said flow tubes and presenting a header wall with an interiorsurface, a pipe disposed in an opening through said header wall, and atransition by extending said header wall into said pipe around saidopening to present an expanding flow control surface between said pipeand said interior surface of said header wall for conveying the heatexchange medium closely over said control surface between said interiorsurface and said pipe to reduce turbulence and pressure loss at saidtransition between said interior surface and said pipe.
 2. An assemblyas set forth in claim 1 wherein said flow control surface is internalwith said header wall and expands radially as it opens axially into saidinterior surface of said header wall.
 3. An assembly as set forth inclaim 2 wherein said flow control surface extends in a circle about anaxis for defining a collar for receiving said pipe.
 4. An assembly asset forth in claim 2 wherein said control surface extends through aradius.
 5. An assembly as set forth in claim 2 wherein said controlsurface extends through a cone to define a chamfer.
 6. An assembly asset forth in claim 2 wherein said pipe and said header wall comprise anorganic polymeric material.
 7. An assembly as set forth in claim 2wherein said pipe and said header wall comprise metal.
 8. An assembly asset forth in claim 3 wherein said pipe terminates in spaced relationshipto the plane of said header wall.
 9. An assembly as set forth in claim 3wherein said pipe includes a bead abutting said collar.
 10. An assemblyas set forth in claim 3 wherein said collar and said pipe are bondedtogether.
 11. An assembly as set forth in claim 10 wherein said pipe issecured prior to bonding to said collar.
 12. An assembly as set forth inclaim 3 wherein said pipe is flared outwardly and engages the exteriorof said collar defining said control surface.
 13. An assembly as setforth in claim 12 wherein said pipe includes an enlarged end defining ashoulder for surrounding and engaging the exterior of said collar withsaid shoulder abutting said collar.
 14. An assembly as set forth inclaim 12 wherein said pipe and said collar include mating undulationsextending annularly thereabout for locking said pipe to said collar. 15.An assembly as set forth in claim 4 wherein said control surfacepresents a smooth transition from said pipe into said interior surfaceof said header wall with a radius or a 30° to 60° chamfer equal to orgreater than 2.0 mm
 16. An assembly as set forth in claim 5 wherein saidcontrol surface presents a smooth transition from said pipe into saidinterior surface of said header wall with a radius or a 30 to 60 chamferequal to or greater than 2.0 mm.